Field imager

ABSTRACT

A detection apparatus for detecting the presence of a sample, the detection apparatus comprising a chamber, ports for introducing a sample within the chamber, an actuation unit for establishing a controllable electromagnetic field in the chamber; and a sensing unit for sensing changes in the electromagnetic field due to the presence of the sample within the chamber. The sensing unit comprises a sensor device comprising a source and a drain embedded in a FET a gate for the FET, in which the gate is formed of a material whose conductivity is related to the electromagnetic field established in a nonconductive medium in contact with the gate.

BACKGROUND OF THE INVENTION

The behavior of matter in electrical or magnetic field, especiallynonuniform fields, is of interest to scientists of various branches:Physics, chemistry, engineering, or life sciences. To chemists andphysicists, it's a science of many and varied phenomena. To engineers,it's a source of new and useful techniques for separating, levitating,and rotating materials or improving material behavior.

In recent decades, Dielectrophoresis has become a fairly well knownphenomenon in which a spatially nonuniform electric field exerts a netforce on the field-induced dipole of a particle. Particles with higherpolarizability than the surrounding medium experience positivedielectrophoresis and they move toward regions of highest electric fieldconcentration. Particles less polarizable than the surrounding mediumexperience negative dielectrophoresis, and move towards regions of lowelectric field concentration. The force depends on the induced dipoleand the electric field gradient, not on the particle's charge. Thus,dielectrophoresis has been used to precipitate DNA and proteins, tomanipulate viruses (100 nm diameter), and to manipulate and separatecells and subcellular components such as microtubules.

Dielectrophoretic levitation fulfills a somewhat specialized need amongthe scientific and technical applications for dielectrophoresis. Twotypes of levitation, passive and feedback-controlled may be used tolevitate particles exhibiting, respectively, negative and positive DEPbehavior.

DEP is technologically important in its own right, as evidenced by thenumber of applications in such scientific and technical fields asbiophysics, bioengineering, and mineral separation. As an example, whichis important in cancer treatment, is cell fusion, as discussed by P. T.Gaynor, and P. S. Bodger in “Electrofusion processes: theoreticalevaluation of high electric field effects on cellular transmembranepotentials”, IEE Proceedings-Science, Measurement and Technology, vol.142, no. 2, pp. 176-182, 1995. In this process, the nonuniform electricfield collects some fraction of these cells on electrode surfaces wherecells of the two types inevitably encounter each other and form chains.A serious of short DC pulse is then applied to the electrodes. Thestrong DC field disturbs the membranes in the region of contact betweencells and initiates their merge or fusion. A potential application ofthis technique is the production of antibodies useful in cancer researchand treatment.

Lab-on-a-chip based on DEP phenomenon has become one of the hottestareas of research recently. It has many applications in the biological,pharmaceutical, medical, and environmental fields. These applicationsare characterized by complex experimental protocols, which need bothmicroorganism detection and manipulation. Hence, lab-on-a-chiptechnology needs to integrate functions such as: actuation, sensing, andprocessing to increase their effectiveness. On the other hand,lab-on-a-chip technology holds the promise of cheaper, better and fasterbiological analysis. However, to date there is still an unmet need forlab-on-a-chip technology to effectively deal with the biological systemsat the cell level.

Recently, two different lab-on-a-chip approaches have been proposed byG. Medoro, N. Manaresi, M. Tartagni, and R. Guerrieri, in “CMOS-onlySensors and Manipulation for microorganisms”, Proc. IEDM, pp. 415-418,2000 and by N. Manaresi, A. Romani, G. Medoro, L. Altomare, A. Leonardi,M. Tartagni, and R. Guerrieri in “A CMOC Chip for IndividualManipulation and Detection”, IEEE International Solid-State CircuitsConference, ISSCC 03, pp. 486-488. 2003. The first, which was proposedin 2002, is the first lab-on-a-chip approach for electronic manipulationand detection of microorganisms. The proposed approach combinesdielectrophoresis with impedance measurements to trap and move particleswhile monitoring their location and quantity in the device. Theprototype has been realized using standard printed circuit board (PCB)technology. The sensing part in this approach can be performed by anyelectrode by switching from the electrical stimulus to a transimpedanceamplifier, while all the other electrodes are connected to ground. Thesecond lab-on-a-chip, which was proposed in 2003, is a microsystem forcell manipulation and detection based on standard 0.35 μm CMOStechnology. This lab-on-a-chip microsystem comprises two main units: theactuation unit, and the sensing unit. The chip surface implements a 2Darray of microsites, each comprising superficial electrodes and embeddedphotodiode sensors and logic. The actuation part is based on the DEPtechnique. The sensing part depends on the fact that particles in thesample can be detected by the changes in optical radiation impinging onthe photodiode associated with each micro-site. During the sensing, theactuation voltages are halted, to avoid coupling with the pixel readout.However, due to inertia, the cells keep their position in the liquid.

The disadvantage of these lab-on-a-chip microsystems, can be summarizedas follows:

-   -   Based on these two systems, we can detect the position of the        levitated cells. However, we cannot sense the actual intensity        of the nonuniform electric field that produces the DEP force.    -   The measurements here are indirect. In other words, there is no        “real-time” detection of the cell response under the effect of        the nonuniform electric field, as the actuation part is halted        while the sensing part is activated.    -   The sensing part in these two microsystems depends on the        inertia of the levitated cells. In other words, this sensing        approach depends on an external factor, which is the inertia of        the levitated cells. Thus, only cells with higher inertia can be        sensed and detected by using these two Microsystems.

What is needed is a lab-on-a-chip that can be used for directmeasurements, where the variations in the electric field can be sensedand the cell can be characterized while the actuation part is stillactive.

SUMMARY OF THE INVENTION

There is therefore provided, according to an aspect of the invention, asensor device, comprising a source and a drain embedded in a FET; and agate for the FET, in which the gate is formed of a material whoseconductivity is sensitive to an electric, magnetic or electromagneticfield established in a nonconductive medium in contact with the gate.The field may be non-uniform. The FET may comprise two spatiallyseparated gates and two spatially separated drains, with a commonsource. Two sensor devices may be connected, where wherein the FET ofthe first sensor device is a p-type FET and the FET of the second sensordevice is a n-type FET. The sensor device may be connected in an arrayof sensor devices.

According to a further aspect of the invention, there is provided adetection apparatus, the detection apparatus comprising a chamber; aport or ports for introducing a sample into the chamber; an actuationunit for establishing a controllable electromagnetic field in thechamber; and a FET sensing unit for sensing changes in theelectromagnetic field due to the presence of the sample within thechamber. The FET sensing unit may be comprised of sensor devicesdescribed above. The changes in the electromagnetic field sensed by thesensing unit may be used to determine the impedance of the sample, or acharacterization unit may use the changes sensed by the sensor unit tomake a 2D image of the electromagnetic field. The actuation unit may beresponsive to feedback from the sensor device. The actuation unit maycomprise an array of electrodes, for example in a quadrupolearrangement, and the sensing unit may comprise an array of sensorsinterspersed with the array of electrodes. At least one of theelectrodes and sensors may receive power from an electromagnetic source,wherein the electromagnetic energy is directed by mirrors controlled bythe actuation unit, or from a power source controlled by the actuationunit. The electrodes may be elongate members, the elongate membersreceiving power at one end and generating the electromagnetic field atthe other end in response to the power.

According to a further aspect of the invention, there is provided amethod of detecting a sample using dielectrophoresis, using the sensordevice and detection apparatus described, where the electromagneticfield is generated and the changes in the electromagnetic field aresensed simultaneously. The particle may be organic matter or a cell.

Other aspects of the invention will be found in the detailed descriptionand claims that follow.

BRIEF DESCRIPTION OF THE DRAWINGS

There will now be given a detailed description of preferred embodimentsof the invention, with reference to the drawings, by way of illustrationonly and not limiting the scope of the invention, in which like numeralsrefer to like elements, and in which:

FIG. 1 a is a block diagram of an apparatus constructed in accordancewith the teachings of the present invention;

FIG. 1 b is a schematic view of actuation and sensing units used in anembodiment of the invention;

FIG. 2 shows light-based electrodes used in the actuation unit;

FIG. 3 shows light beam controlled driving circuits for the electrodesin the actuation unit;

FIG. 3 a shows light beam controlled driving circuits for an array ofelectrodes in the actuation unit;

FIG. 4 shows various shapes of the tip of the electrode;

FIG. 5 is a perspective view of the physical structure of an eFET;

FIG. 6 is the circuit equivalent of an eFET;

FIG. 7 is the circuit symbol for an eFET;

FIG. 8 is the circuit symbol of a DeFET;

FIG. 9 is the circuit equivalent of a DeFET;

FIG. 10 is the Current-Mode Instrumentation Amplifier (CMIA) circuitused as a readout circuit;

FIG. 11 a is a perspective view of a representation of the quadrupoleand DeFET;

FIG. 11 b is a point charge representation of the quadrupolearrangement;

FIG. 11 c shows a large quadrupole configuration of electrodes;

FIG. 11 d is a schematic of a single large quadrupole electrode usingmetal2 strips;

FIG. 11 e shows a centric configuration for light beam controlleddriving poles with the sensor;

FIG. 12 is a graph displaying simulation results using Coulomb Software;

FIG. 13 is a schematic representation of a DeFET according to theinvention;

FIG. 14 is a graph showing simulation results using Cadence Simulator;

FIG. 15 is a graph showing the frequency response of the CMIA used inthe simulation;

FIG. 16 is a graph showing the different common mode rejection ratio(CMRR) for different CMIA circuits; and

FIG. 17 is a schematic of a DeFET acting as an impedance sensor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The electric field imager disclosed herein is based on conventional TSMC0.18 μm CMOS technology. Some simulation and experimental results arepresented at the end of the disclosure. Referring now to FIG. 1 a, theproposed microsystem 10 comprises (a) an actuation unit 12, which is ina quadruple electrode configuration as shown in FIG. 1 b to produce therequired DEP force to levitate the sample, for example, a cell, that wewant to characterize; (b) a sensing unit 14, which is a DifferentialElectric Field Sensitive Field Effect Transistor (DeFET), where, toobtain an image of the electric field, and characterize the levitatedcell, the DeFET is used in an array form, and the read out circuit [i.e.the electric field-to-voltage converter (E-to-V converter) circuit] ison a chip; (c) a characterization unit 16 to analyze the images anddetermine characteristics of the sample; (d) a chamber 18 to hold thesample with ports for inserting the sample; and (e) a controller 20 forcontrolling the actuation unit 12. The controller 20 may be programmedto create a specific non-uniform field, and may operate based uponfeedback from the sensing unit 14 or the characterization unit 16. Eachcomponent may be located in any convenient location, such as under,inside or outside the chamber. Also, while the actuation unit 12 andsensing unit 14 are shown as separate bodies, it will be understood thatthey may occupy the same space as shown in FIG. 1 b. The chamber 18 hasports 22 for introducing a sample. As described, the apparatus 10 iscapable of simultaneously actuating, sensing, and manipulating thesample in the chamber 18, and can be used to process samples such ascells, particles, liquids, powder, organic matter, bio-live or deadspecies, or other types of samples. In this document, processing asample includes, but is not limited to, actuating, sensing, testing,levitating, separating, manipulating, isolating, trapping, analyzing, oridentifying the sample as a whole or a part thereof, performedindividually, or in combination. It will also be understood that when anelectric field is referred to, the discussion may equally apply tomagnetic fields, or electromagnetic field, since a time varying electricfield will have a magnetic field component. Each of the componentspresented above will now be discussed in more detail.

The Actuation Unit

The actuation unit 12 comprises poles 24, or electrodes, that generatethe electric field in the chamber 18. The poles 24 are spatiallydistributed as shown in FIG. 1 b and produce the required force toprocess a sample (not shown). Sensors 28 are also spatially distributed.Each pole 24 and sensor 28 is connected to a corresponding terminal 25to allow them to be individually addressed. Referring to FIG. 11 a, thesample 26 is shown in the center of four poles 24 with sensors 28 below.Referring again to FIG. 1 b, each pole 24 can be individually addressedand actuated using electrical signals, a light beam such as a laser, orother sources of energy, such as a magnetic source connected toterminals 25 to produce the desired field and therefore operate on thesample 26. In the case of the laser, the light beam will use a set ofmirrors and lenses to focus the beam on the electrode to be actuated.FIG. 2 shows the light-based electrodes 24 and FIG. 3 shows the drivingcircuits 34 where the light beam 36 controls a switch 38 that adjuststhe voltage at the top of the pole 24, which in turn affects theelectric field and corresponding DEP force that is generated between thepole 24 and the grounded plate 78 on the other side. Mirror 80 andlenses 82 are shown directing the beam 36. The arrangement used may be amuch more complex system, where the position of mirrors 80 and lenses 82are controlled to address individual poles 24. The cross-section of thetip of pole 24, where the force is generated, can be hexagonal, square,rectangular, or other shapes, with examples shown in FIG. 4. Each pole24 may be programmed to adjust its value based on the readout of thesensing unit 14 to create a feedback loop that can verify the exactvalue of the generated force.

FIG. 3 a shows the spatial distributed poles to generate an arbitraryelectric field by controlling the values of the volt at the individualelectrodes. The poles 52, 54, 56, and 58 are similar to theconfiguration in FIG. 3 but with different height to enable singleaddressable poles. The pole 52 that is closer to the light source isshorter than the far poles (54 and 56) in the other raw. The poles inthe same row 56 have the same height to simplify the addressingmechanism. A light or energy source 30 is used to control the volt atthe pole. The energy will be modulated using a modulator 35. Amicro-mirror array 40 is used to direct the energy to a switch 38 inFIG. 3. Each micro-mirror is separately controlled or programmable toreflect the light or the energy to a specific pole. The energy beams 45reflected from the mirror and falling on the switch at each pole willcontrol the voltage (driven from the voltage source 38) at the electrodetip. The actuation pole can be various shapes and concentric as shown inFIG. 11 e. Each electrode should have a metallic tip.

Referring now to FIG. 11 b, the actuation poles 24 in the quadrupoleconfiguration shown in FIG. 11 a are approximated by a system of fourpoint charges 39 (±Q) located in the x-y plane and arrangedsymmetrically about the z-axis. Due to symmetry, the radial component ofthe force is zero (i.e. F_(ρ)=0), and the z-component of the DEP forceis defined by the following equation:

${\frac{F_{z}}{a^{5}} \cong {{- \frac{3\; Q^{2}}{\pi \; ɛ_{1}}}{{Re}\lbrack K_{2} \rbrack}\frac{( {z/b} )}{{b^{7}( {1 + ( {z/b} )^{2}} )}^{6}}}} = {{- \frac{3\; Q^{2}}{\pi \; ɛ_{1}}}{{Re}\lbrack K_{2} \rbrack}{G_{QUAD}(z)}}$

where G_(QUAD)(Z) collects the geometric dependencies and

$K_{2} = \frac{10( {ɛ_{p}^{*} - ɛ_{m}^{*}} )}{{2\; ɛ_{p}^{*}} + {3\; ɛ_{m}^{*}}}$

where ∈*_(p) is the complex permittivity of the cell with radius aimmersed in a media with complex permittivity ∈*_(m). From the firstequation, we can observe that the force F_(z) is proportional to a⁵(radius)⁵, so we can levitate the small particles using thisconfiguration. On the other hand, the quadrupole levitator comprises anazimuthally symmetric electrode arrangement capable of sustainingpassive stable particle levitation. Also, as a diagnostic tool,quadrupole levitation offers researchers insight into the detailedelectrical composition of materials. For these reasons, we selected thequadrupole electrode configuration as an actuation part in our design.It will be apparent to those skilled in the art that other designs mayalso be used.

To implement a large (100 um) quadrupole system in the 0.18 CMOStechnology, we are using four identical octagons using metal2 layer.These octagons are in the x-y plane and arranged symmetrically about thez-axis (see FIG. 11 a), with a distance 100 cm between each other, asshown in FIG. 11 c. FIG. 11 d shows a schematic diagram of a singleelectrode. The dimension of the electrode is 100 μm×100 μm from edge toedge. This dimension violates the direct rule check (DRC) of thestandard 0.18 μm technology, for which the maximum metal area should be<35 μm×35 μm. Thus, we used a grid or mesh arrangement of metal2 thatleaves a 1 μm space between each metal2 rectangle, as shown in FIG. 11d. Individual strips 27 of metal2 overlap each other and are spaced withgaps between them to form a mesh electrode. FIG. 11 e shows a concentriccontinuous pole 50 with embedded sensors 60. The poles have differentheights. The inner pole has light sensitive switch 42, the outside polehas switch 48 and the in-between two poles have the switches 44 and 46.The poles are connected to a voltage source 38. The shape in FIG. 11 eis octagonal because it is easier to fabricate in 0.18 um standard TSMCtechnology, but any other shape can be used. It is worth noted that thecontinuity of the electrodes generate a better and more accurate planarelectric field.

The Sensing Unit

The sensing unit 14 is composed of an array of the Differential ElectricField Sensitive MOSFET (DeFET) 40 shown in FIG. 8 acting as sensorelements 28 in FIG. 1 b. DeFETs 40 allow us to record accurateinformation about the in-situ intensity of the applied nonuniformelectric field. Referring to FIG. 1 b, the sensor elements 28 areindividually addressable through terminals 25 to read individual sensorvalues. As discussed above for the actuation unit 12, each sensor 28 maybe actuated using electrical signals or a light beam, such as a laser.The sensors 28 are located in convenient locations around where thesample 26 will be processed by the actuation unit 12, such as in thespace between the actuation electrodes 24 so that measurements aroundthe characteristics of the sample 26 are recorded, and the intensity ofthe applied non-uniform electric field and force. More detail will nowbe given on the construction and operation of the DeFET 40.

The Electric Field Sensitive Field Effect Transistor (eFET)

In the DEP levitation process, the manipulating electric field is anonuniform electric field (i.e. the electric field is a function of thedistance). Thus, we can detect the electric field by using the ElectricField Sensitive MOSFET (eFET) 42 shown in FIG. 5 as a novel electricfield sensor. FIG. 5 shows the physical structure of the eFET 42. It hastwo adjacent drains 44, two adjacent floating gates 46 on silicon oxide(SiO₂) layers 47, and one source 48. For the eFET 42, it is equivalentto two identical enhancement MOSFET devices, as shown in FIG. 6. Thus,the two drain currents are equal if no electric field applied. Under theinfluence of a nonuniform electric field, a current imbalance betweenthe two drain currents occur. Due to the drain current dependence on thegate voltage, the eFET device 42 that has two adjacent gates 46, and twoadjacent drains 44, but isolated and spatially separated from eachother, can sense the difference between the two gate voltages, whichreflects the intensity of the applied nonuniform electric field betweenthe two locations of the gates 46. FIG. 7 shows the circuit symbol ofthe eFET 42. To increase the dynamic range of the eFET 42, the CMOSconcept is used to implement the DeFET 40 sensor, and this sensor may beused as the basic sensing block in the electric field imager. If onlyone side of the eFET were present (i.e. one gate 46, one drain, 44, andthe source 48), the drain current would still be related to the electricfield that is present, however, there would be nothing to compare thevalue with. This would be useful if a proper calibration technique wasused. More accurate and meaningful results are therefore obtained usingthe eFET 42 as described, with a fixed distance between gates 46.

The Differential Electric Field Sensitive MOSFET (DeFET)

Referring to FIG. 8, the DeFET 40 is formed of two complementary eFETs42, one of them is a p-type eFET 42 and the other is an n-type eFET 42.The equivalent circuit of the DeFET 40 is shown in FIG. 9. Referring toFIG. 9, the two gates 46 of the p-type eFET 42 and n-type eFET 42 areconnected with each other, and there is a cross coupling between the twodrains 44 of the p-type eFET 42 and the n-type eFET 42. The outputcurrent I_(O) is equal to the difference between the two drain currentsI_(D2)−I_(D3) (i.e. I_(O)=I_(D2)−I_(D3), see FIG. 9). On the other hand,I_(D2) and I_(D3) are functions of the two applied gate voltages V_(in1)and V_(in2), respectively, so, I_(O) is directly related to thedifference between the two applied gate voltages (V_(in1)−V_(in2)), andV_(in1)−V_(in2) is equal to the applied electric field above the twogates 46 multiplied by the distance between them (V_(in1)−V_(in2)/d=E),where d is the distance between the two split gates 46, which isconstant. So, I_(O) is related directly to the intensity of the appliednonuniform electric field. Thus by measuring I_(O) we can detect theintensity of the nonuniform electric field.

The Read-Out Circuit

For the read-out circuit 50, a higher differential gain is needed toamplify the small current signal at the output; also, it has to have ahigh common mode rejection ratio (CMRR) to reject any common modesignal. Referring to FIG. 10, a suitable read-out circuit 50 is theCurrent-Mode Instrumentation Amplifier (CMIA) proposed by Yehya H.Ghallab, Wael Badawy, Karan V. I. S. Kaler and Brent J. Maundy in “ANovel Current-Mode Instrumentation Amplifier Based on OperationalFloating Current Conveyor”, submitted to IEEE Transaction ininstrumentation and measurement, (33 pages), January 2003. It is formedof two operational floating current conveyors (OFCC) 52, two feedbackresistors (R_(W1) and R_(W2)) 54, a gain determined resistor (R_(G)) 56and a ground load (R_(L)) 58.

The Characterization Unit

The characterization unit 16 reads the output of the sensors 28 anddevelops a 2D image for the values and compares it with the actuatedvalue. The difference between the actuation values and the sensed valuesare used to detect and characterize the levitated sample 26 and thecharacteristics of the contents and liquid inside the micro-channelwhich may be used as the chamber 18. The characterization unit 16 canalso use a sequence of images and process them using image and videoprocessing algorithms to identify the contents of the sample, algorithmssuch as edge detection, motion tracking, or DSP techniques.

The Controller

The controller 20 adjusts the value of the actuation unit 12 so itgenerates the required force. The controller 20 may adjust the actuationvalues using preprogrammed values, or it can read values from thesensing unit 14 or the characterization unit 16 to adjust the actuationunit 12 if needed.

Sensor-Actuation Integration

The integrated quadruple poles 24 with the sensing unit 14 is shown inFIG. 11 a. It shows the quadrupole configuration to levitate the samplewith the proposed electric field sensors 28 (DeFET 40) implanted in themiddle. FIG. 12 shows the simulation results with the electric fieldsensors, represented by line 74 and without the electric field sensors,represented by line 76. From FIG. 12, we can observe that:

a) The Electric field sensors didn't disturb the profile of the electricfield; alternatively, it improves the profile as we under a very smalllevitation height (Z=3 μm) the levitated particle is on the stable rangeof operation. In other words, the insertion of the DeFETs reduces theappearance of the unstable regime of operation, thus, we can easilylevitate the cells can passively.

b) The z component of the dielectrophoretic force is increased, so wecan levitate the heavy cells without any need of any other externalforces, also, we can levitate the cell far from the electrodes, so manyprocesses can be done (e.g. cell fusion, . . . etc.).

The sensing part (i.e. DeFET) is analyzed, designed, simulated, andimplemented using Cadence analog design tool. The schematicrepresentation of a single DeFET 40 is shown in FIG. 13, and thesimulation results which confirm the functionality of the DeFET is shownin FIG. 14, where the different lines show different variations betweenthe gates ranging from 3V (top line) to −3V (bottom line). From thisfigure, we can observe the linear relationship between the outputcurrent and the variation of the two gate voltages, which can reflectthe variation with the applied electric field above the gates.

DeFET as an Impedance Sensor

We can also use a DeFET 40 as an impedance sensor by using the techniqueshown in FIG. 17. In this figure, an excitation electrode 60 is used totrap the sample 26, in this case, a biocell, between it and the DeFET.The output current of the DeFET 40 is connected to a transimpedanceamplifier 62 to convert the output current into voltage. In thistechnique, by measuring the output voltage, we can determine theimpedance of the trapped biocell 26. The mathematical derivation isshown below.

Here we have a biocell 26 above the DeFET 40, so the output voltage(V_(owcell)) is related to V_(in) by the equation:

$V_{owcell} = {\frac{V_{i\; n}}{R_{sen} + ( {R_{cell}//C_{cell}} )}( {R_{F}//C_{F}} )}$

where R_(F) is the feedback resistance, C_(F) is the feedbackcapacitance, R_(sen) is the output resistance of the DeFET 40, R_(cell)is the biocell 26 resistance, and C_(cell) is the biocell 26capacitance. To get R_(sen), we will determine the output voltagewithout the biocell 26, and the above equation will be:

$V_{o} = {\frac{V_{i\; n}}{R_{sem}}( {R_{F}//C_{F}} )}$

From the above equation, we can get R_(sen), so we can simply use thisvalue in the first equation to get the impedance of the biocell (i.e.R_(cell)//C_(cell)).

Simulation

To verify the operational characteristics of the proposed read outcircuit 50, a simulation was developed using PSPICE version 7.1. Then,the proposed CMIA was prototyped and the simulation results wereverified. The proposed current-mode instrumentation amplifier (CMIA) isshown in FIG. 10. It uses two OFCC 52. Each OFCC is constructed using acurrent feedback op amp 64 (such as serial no. AD846AQ,) andcurrent-mirrors composed of transistor arrays 66 (such as a device fromHarris, serial no. CA3096CE,). From FIG. 15, we can observe that theexperimental results validate the simulated results, and by usingexternal resistors, simply, we can control the gain. To measure thecommon-mode rejection ratio (CMRR) of the circuit in FIG. 10, weconnected both v_(in1) and v_(in2) together to the same input voltagesource. CMRR was measured experimentally as a function of frequency fora differential voltage gain of 20. The result obtained is plotted inFIG. 16. From FIG. 16, we can see that the proposed topology shows CMRRmagnitude and bandwidth is ≈76 dB@185 KHz. In FIG. 16, a comparisonbetween the proposed and the currently used CMIA is done. We can observethat the proposed CMIA circuit has higher CMRR as well a higherbandwidth associated with this CMRR as shown by line 68 than othertopologies, where line 70 is from A. A. Khan, M. A. Al-Turaigi and M.Abou El-Ela, in “An Improved Current-mode Instrumentation Amplifier withBandwidth Independent of gain,” IEEE Trans. Instr. Meas., vol. 44, no.4, 1995, and line 72 is from B. Wilson in “Universal ConveyorInstrumentation Amplifier,” Elect. Let., vol. 25, no. 7, pp. 470-471,1989 and S. J. G. Gift, in “An Enhanced Current-Mode InstrumentationAmplifier,” IEEE Trans. Instr. Meas., vol. 50, no. 1, pp. 85-88, 2001.So this CMIA is the best choice for our design.

Immaterial modifications may be made to the invention described herewithout departing from the invention. In the claims, the word“comprising” preceding a listing of claim elements does not excludeother elements being present in the method or apparatus referred to. Inthe claims, the use of the indefinite article preceding an element doesnot exclude more than one of the element being present.

1-10. (canceled)
 11. A detection apparatus for detecting the presence ofa sample, the detection apparatus comprising: a chamber; a port forintroducing a sample within the chamber; an actuation unit forestablishing a controllable electromagnetic field in the chamber; and aFET sensing unit for sensing changes in the electromagnetic field due tothe presence of the sample within the chamber.
 12. The detectionapparatus of claim 11, wherein the electromagnetic field is spatiallynon-uniform.
 13. (canceled)
 14. (canceled)
 15. The detection apparatusof claim 11 wherein the sensing unit further comprises a first sensordevice made of a first FET connected to a second sensor device made of asecond FET, the first FET being a p-type FET and the second FET being an-type FET.
 16. The detection apparatus of claim 11 wherein the sensingunit comprises an array of sensor devices.
 17. The detection apparatusof claim 11, wherein the actuation unit comprises an array of electrodesand the sensing unit comprises an array of sensors interspersed with thearray of electrodes.
 18. The detection apparatus of claim 17, wherein atleast one of the electrodes and sensors receive power from aelectromagnetic source, wherein the electromagnetic energy is directedby mirrors controlled by the actuation unit.
 19. The detection apparatusof claim 17 wherein at least one of the electrodes and sensors receivespower from a power source controlled by the actuation unit.
 20. Thedetection apparatus of claim 19 wherein the electrodes are elongatemembers, the elongate members receiving power at one end and generatingthe electromagnetic field at the other end in response to the power. 21.The detection apparatus of claim 17, wherein the electrodes comprise ametal mesh.
 22. The detection apparatus of claim 17, wherein theelectrodes have metallic tips.
 23. The detection apparatus of claim 11wherein the actuation unit comprises an array of electrodes.
 24. Thedetection apparatus of claim 23 wherein the array of electrodes isarranged in a quadrupole arrangement.
 25. The detection apparatus ofclaim 11 wherein the changes in the electromagnetic field sensed by thesensor device are used to determine the impedance of the sample.
 26. Thedetection apparatus of claim 11 further comprising a characterizationunit that uses the changes sensed by the sensor unit to make a 2D imageof the electromagnetic field.
 27. A method of detecting a sample usingdielectrophoresis, the method comprising the steps of: introducing thesample within a chamber; using an actuation unit to establish acontrollable electromagnetic field in the chamber; and using a FETsensing unit to simultaneously sense changes in the electromagneticfield due to the presence of the sample within the chamber.
 28. Themethod of claim 27 wherein the actuation unit is responsive to feedbackfrom the sensor device.
 29. The method of claim 27 wherein the actuationunit establishes a spatially non-uniform electromagnetic field.
 30. Themethod of claim 27, wherein using a FET sensing unit comprises providinga sensor device comprising: two spatially separated drains embedded in aFET; two spatially separated gates for the FET, in which the gate isformed of a material whose conductivity is sensitive to theelectromagnetic field established in a nonconductive medium in contactwith the gate; and a common source embedded in the FET;
 31. The methodof claim 30 wherein the FET sensing unit comprises a p-type FET and ann-type FET.
 32. The method of claim 27 wherein using a FET sensing unitcomprises using an array of sensor devices.
 33. The method of claim 27wherein using an actuation unit comprises using an array of electrodes.34. The method of claim 27, wherein using an actuation unit comprisesusing an array of electrodes and using a sensing unit comprisesinterspersing an array of sensors with the array of electrodes.
 35. Themethod of claim 33 wherein using an array of electrodes comprisesarranging the electrodes in a quadrupole arrangement.
 36. The method ofclaim 34, wherein using an actuation unit and using a sensing unitfurther comprises powering at least one of the electrodes and sensorsusing electromagnetic energy wherein the electromagnetic energy isdirected by mirrors controlled by the actuation unit.
 37. The method ofclaim 27 wherein the sample is organic matter.
 38. The method of claim27 wherein the sample is a cell.
 39. The method of claim 27 furthercomprising the step of using the changes in the electromagnetic fieldsensed by the sensing unit to make a 2D image of the electromagneticfield.
 40. The method of claim 27 further comprising the step of using acharacterizing unit to determine the impedance of the sample using thechanges sensed by the sensing unit.